linux crash course chapter 03 3

ls: LiSt files• Used to list files contained in a directory • Can narrow the search using pattern matching • Examples – ls  displays ‘all’ the files in the directory – ls cats  display

Chapter 3:

Command Line Utilities

Doin’ stuff

Typing Commands

• Beware of special characters

• Characters that have special meaning to the shell

• Shell expands, modifies and interprets

special characters before issuing the

command

Special Characters

• & ; | * ? ‘ “ ` [ ] ( ) $ < > { } ^ # / \ % ! ~ +

• Plus whitespace (tabs, spaces, newlines)

• Do not use these in filenames unless you

have to

• To use them, either put in single quotes,

or proceed with a backslash

– ls ‘filename with special chars!!’

– ls \[cat\]

Special Characters con’t

• All special characters have special meaning

to the shell

• We’ll explore these in great detail in

upcoming chapters

• Linux & Unix come with thousands of utilities

• Some used explicitly, others implicitly

• Some text-based, some GUI, some both

Some tips before we start

• Tab completion

– When typing a filename or command name, you can type the first few letters then hit TAB to auto- complete the command

• Pipe (|) symbol

– Used to chain commands together

– The output of one command becomes the input

of another

– We’ll revisit this in detail later

ls: LiSt files

• Used to list files contained in a directory

• Can narrow the search using pattern

matching

• Examples

– ls  displays ‘all’ the files in the directory

– ls cats  displays the file cats in the directory – ls ca*  displays files starting with ‘ca’

cat: catenate a file

• Displays the contents of one or more files

• Beware – don’t try with binary files

• Examples

– cat myfile  displays contents of myfile

– cat file1 file2  displays contents of file1

followed by contents of file2

rm: ReMoves a file

• Similar to del in DOS

• Use the –i option to invoke interactive mode,

which prompts you if you’re sure

• Examples:

– rm myfile  deletes myfile

– rm –i myfile  prompts you before deleting

more and less: pagers

• more and less are similar in that they both break up long files into page long chunks

• Press h to display possible commands

• Examples

– less myfile  displays myfile one page at a

time

cp: CoPies files

• Usage: cp sourcefile destinationfile

• Creates a copy, leaves sourcefile intact

• If destinationfile exists, it will be overwritten

– Unless you use –i option

• Example:

– cp myfile myfile.backup

mv: MoVe files / change name

• Usage: mv existingfile newfile

• Just like cp, can overwrite with –i option

• Renames a file, which can also move it to another directory

• Examples:

– mv myfile foshizzle

– mv /dir1/myfile /dir2/myfile

lpr: Line PRinter

• Places files into the print queue

• Usage: lpr [-Pprintername] files

• You can check the status of queue with lpq

• You can delete a job with lprm

• Sorry, we don’t have a printer

grep: global regular expression print

• Used to search for strings in files/output

• Usage: grep expression filename

• Returns lines with expression in filename

• Example:

– grep ‘automagically’ myfile

head: display beginning

• Displays beginning of file

• head -X filename displays first X lines

• Check out pg 727/691 for more options

tail: duh

• Displays the end of a file

• tail -X myfile displays the last X lines

• Check out pg 843/783 for more options

sort: displays sorted info

• sort displays data in a sorted manner, without altering the original file

• Lots of options – sort alphabetically,

numerically, with or without repeats, reverse order, etc

• Check out pg 817/762

uniq: removes duplicates

• uniq displays data, omitting successive

file: what kind of file is this?

• Usage: file filename

• Tells you what kind of file you’re working with and what kind of data is in it

• Examples include program, shell builtin,

ASCII text, compressed data, etc

echo: display text

• Displays (echoes) text back to the terminal screen

• Can print out contents of shell variables

• Useful in shell scripts

• In other words, seems dumb now but we’ll use it a lot down the road

date: displays time and date

• Command options can change formatting

• Privileged accounts can use date to change date and time

• Can be useful for scripting

script: captures session

• Captures all input and output on the terminal and saves to a file

• A good way to document your work, or

capture errors for analysis

• Type script to start capture, exit to quit

• By default stores everything in the file

typescript

Text Converters

• unix2dos and dos2unix

• Unix and DOS use different end of line

characters

• Use these utilities when moving text files

back and forth between Windows and Linux systems

• Weird script error? Try dos2unix

Uncompressing files

• bunzip2 compressed-file

• gunzip compressed-file

• ucompress compressed-file

tar: Tape ARchive

• Packs and unpacks files from archives

• *Does not compress, only assembles*

• Tons of options, allowing you to add or

remove files from archive, and also apply compression using third party support

which: locates utilties

• Will display the location of a utility

• which ls  displays location of ls command

you’re using

• In case of there being multiple locations,

which only displays the first (i.e., the one

you will be using)

whereis: locates utilities

• Similar to which, but displays the utilities in a

standard set of locations

• The first one listed may not be the one you

will issue when you enter the command

• All depends on your PATH (chapter 4)

• which and whereis do not list shell builtins

• Shell builtins are functions that are internal to the shell itself – no binary executable

• To see if you’re using a builtin, use type

apropos: what do I use?

• Not sure what utility you’re looking for?

• Try apropos keyword

• Displays utilities and libraries related to your keyword

• Found one, but not sure? whatis utility to

show what it does, or check man page

locate: search for files

• System maintains a database of files

• Your system administrator should configure a job to regularly update this database

• Searches for any kind of file – not just utilities

• Some systems use slocate (secure)

• Latest distros use mlocate via locate

who: Who’s online?

• Displays what users are logged on

• Also displays when they logged on, and with what device (terminal or console, etc)

• Also try who am i

finger: reach out and touch …

• finger by itself displays users logged on like

who, but also shows idle time and office

location

• finger username shows info about that user,

like home directory, last logon, their shell, if they have unread mail, and plan and project files

write: send a message

• write username opens up a text-based chat

with the user

• Type message

• Wait for response

• CTRL-D to exit write

mesg: Enable/disable write

• Usage: mesg y|n

• Turns off whether users can write you or not

• Useful if you don’t want to be bugged

mail: system mail

• Our system is a closed system

• You can send mail to other users on the system

• No public mail